In the treatment of raw municipal wastes for sanitary disposal, there results at least one stream of waste sludge containing suspended solids in concentrations usually in the range of 1 to 5 percent by weight. To prevent contamination of available water supply local ordinances usually prohibit the disposal of such sludges without further treatment. In larger communities having complete facilities for municipal waste disposal, the aforementioned waste sludges are often digested in a digester for anaerobic decomposition of the suspended organic material into an odorless and non-putrescible residue, which can be disposed of without any problem. The mixture of carbon dioxide and methane resulting from the digestion is easily burned and can be used for heat and power production. Where no such complete facilities are available and the direct disposal of waste sludges into the immediate environment is not permitted, the sludges must be treated either to remove the solids from the water phase or to concentrate the sludges sufficiently to permit transport of the solids or the concentrated sludges to a remote treatment facility or landfill area, where safe disposal can be made without causing health hazards.
A serious problem in these circumstances is the extreme difficulty encountered in concentration of the waste sludges, which do not settle or filter readily. Some improvement in settling rate is had by adjusting the pH to a value in the alkaline range, e.g. at a pH of 11. Chemical precipitation has also been suggested for the purification of sewage. This involves the use of a compound such as alum which forms a gelatinous precipitate under alkaline conditions and which acts as an adsorbent for the impurities. A coagulant or flocculating agent is usually added to increase the particles size of the impurities. However, waste sludges thus conditioned can only be dewatered by filtration with extreme difficulty, and the solids content of the sludge after dewatering is considerably less than 15 percent by weight. The disposal thereof is still a problem in that the high water content precludes the disposal by incineration and that transport of the sludge to a safe disposal is not economically feasible.
It is therefore an object of the present invention to provide a process for the concentration of municipal waste sludges for the recovery of suspended solids at higher concentrations than heretofore possible.
Another object of the invention is to provide an economically feasible process for the disposal of municipal waste sludges.
It is also another object to provide a process for dewatering municipal waste sludges to a solids content sufficiently high to enable incineration of the dewatered sludge.
It is further object to provide an economical waste treatment process of municipal sludges wherein chemical consumption is kept to a minimum.
Further objects will become apparent from the following description and appended claims.